1. Technical Field of the Invention
The present invention relates to a gas treatment system for use in separating and recovering gaseous hydrocarbon (e.g., vapor of toluene, xylene, or the like employed as a solvent) contained in a treatment-object gas such as factory exhaust gas. More particularly (see FIG. 4), the invention relates to a gas treatment system comprising: a rotary adsorbing-desorbing concentration device 1 including a gas-permeable adsorbing rotor 4 having adsorbent as a main component thereof, the rotor 4 having in a rotational region thereof an adsorbing area x for allowing passage of treatment-object gas A containing gaseous hydrocarbon through a rotor portion corresponding thereto and a desorbing area y for allowing passage of desorbing-concentrating gas B through a rotor portion corresponding thereto, the adsorbing area and the desorbing area being arranged side by side and separated from each other along a rotational direction of the rotor;
an adsorbing-desorbing recovery device 2 for selectively effecting an adsorbing process for causing the desorbing-concentrating gas Bxe2x80x2 past the desorbing area y to pass an adsorbent layer 9 and a desorbing process for causing desorbing-recovering gas C to pass the adsorbent layer 9; and
a condensing recovery device 3 for cooling adsorbing-recovering gas Cxe2x80x2 past the adsorbing layer 9 so as to condense the gaseous hydrocarbon contained therein and then separating and recovering this condensed hydrocarbon from the gas.
2. Description of the Related Art
Conventionally, with a gas treatment system of the above-noted type, as shown in FIG. 4, the desorbing-concentrating gas Bxe2x80x3 which has adsorbed and separated the hydrocarbon from the treatment-object gas A from the rotary adsorbing-desorbing concentration device 1 in the course of passage thereof through the adsorbent layer 9 (the layer 9 shown on the right-hand side in FIG. 4) engaged in the adsorbing process at the adsorbing-desorbing recovery device 2 is directly discharged into the atmosphere together with the treated treatment-object gas Axe2x80x2 discharged from the adsorbing area x of the rotary adsorbing-desorbing concentration device 1 (see Japanese published patent gazette No. Sho. 60-10772).
Regarding the adsorbing-recovering gas Cxe2x80x3 (the gas which has condensed the desorbed hydrocarbon from the adsorbent layer 9 and separated and eliminated it) which has passed the condensing recovery device 3 subsequent its passage through the adsorbent layer 9 (the other layer 9 shown on the left-hand side in FIG. 4) engaged in the desorbing process of the adsorbing-desorbing recovery device 2, there have been proposed various types of adsorbing-desorbing recovery devices designed to return this gas to the adsorbing adsorbent layer 9 (i.e., the adsorbent layer currently engaged in the adsorbing process) (for instance, Japanese laid-open patent gazette No. Hei. 11-57372; Japanese laid-open patent gazette No. Hei. 9-38445; Japanese laid-open patent gazette No. Hei. 6-226029; Japanese published patent gazette No. Hei. 4-66605; and Japanese published patent gazette No. Sho. 53-22541).
Further, for this returning of the desorbing-recovering gas Cxe2x80x3 past the condensing device back to the adsorbing adsorbent layer 9, there is also known an adsorbing-desorbing recovery device including a recycling passage for recycling the desorbing-recovering gas Cxe2x80x2 past the desorbing adsorbent layer 9 again to the same desorbing adsorbent layer 9 and returning a portion of the desorbing-recovering gas taken off this recycling passage back to the adsorbing adsorbent layer 9 via the condensing recovery device 3 (e.g., see Japanese laid-open patent gazette No. Hei. 9-38445 and Japanese laid-open patent gazette No. Hei. 6-226029).
However, in order to reduce the concentration of the hydrocarbon contained in the adsorbing-concentrating gas Bxe2x80x2 (concentrating gas) caused to contain the gaseous hydrocarbon in the course of its passage through the desorbing area y of the rotary adsorbing-desorbing concentration device 1 to a level low enough for the gas to be discharged directly into the atmosphere by means of passage through the adsorbing adsorbent layer 9 of the adsorbing-desorbing recovery device 2, a significantly high treatment efficiency is required of this adsorbing-desorbing recovery device 2. Specifically, the adsorbing-desorbing recovery device 2 needs a large amount of adsorbent, which makes it difficult to form this device compact. Moreover, a significantly high temperature (e.g., high temperature which can not be obtained with a typical steam heat source) is needed for the desorbing process to be effected in the adsorbing-desorbing recovery device 2, which leads to high energy consumption. In addition, such high desorbing temperature disadvantageously promotes degradation of the adsorbent and tends to invite unwanted change in the quality of hydrocarbon, such as a solvent, to be recovered.
Further, as described also hereinbefore, if it is attempted to elevate the cooling temperature needed by the condensing recovery device 3 (to elevate up to substantially the room temperature) by returning the desorbing-recovering gas Cxe2x80x3 past this condensing device 3 back to the adsorbing adsorbent layer 9 (in other words, by allowing un-condensed gaseous hydrocarbon to remain at a certain high concentration in the desorbing-recovering gas Cxe2x80x3 past the condensing device), there exists a limit in possible elevation of the temperature if the hydrocarbon concentration of the desorbing-concentrating gas Bxe2x80x3 past the adsorbing adsorbent layer 9 together with the desorbing-recovering gas Cxe2x80x3 past the condensing device is to be maintained low enough for allowing its discharge into the atmosphere. Hence, the condensing recovery device 3 needs sufficiently low temperature for cooling the gas. In this regard too, the energy consumption is increased disadvantageously.
In view of the above-described state of the art, a primary object of the present invention is to achieve compactness of the system and reduction in energy consumption thereof while retaining high recovery efficiency of the gaseous hydrocarbon by means of reasonable improvement enabling more efficient use of the rotary adsorbing-desorbing concentration device of the system.
For accomplishing the above-noted object, according to the present invention (see FIG. 1 or FIG. 3), a gas treatment system comprises:
a rotary adsorbing-desorbing concentration device 1 including a gas-permeable adsorbing rotor 4 having adsorbent as a main component thereof, the rotor 4 having in a rotational region thereof an adsorbing area x for allowing passage of treatment-object gas A containing gaseous hydrocarbon through a rotor portion corresponding thereto and a desorbing area y for allowing passage of desorbing-concentrating gas B through a rotor portion corresponding thereto, the adsorbing area and the desorbing area being arranged side by side and separated from each other along a rotational direction of the rotor;
an adsorbing-desorbing recovery device 2 for selectively effecting an adsorbing process for causing the desorbing-concentrating gas Bxe2x80x2 past the desorbing area y to pass an adsorbent layer 9 and a desorbing process for causing desorbing-recovering gas C to pass the adsorbent layer 9; and
a condensing recovery device 3 for cooling adsorbing-recovering gas Cxe2x80x2 past the adsorbent layer 9 so as to condense the gaseous hydrocarbon contained therein and then separating and recovering this condensed hydrocarbon from the gas;
wherein the system further comprises a desorbing-concentrating gas return passage 12 for returning desorbing-concentrating gas Bxe2x80x3 past the adsorbent layer 9 after the desorbing layer y to cause this desorbing-concentrating gas Bxe2x80x3 together with the treatment-object gas A to pass the adsorbing area x.
That is, according to the above construction (see FIG. 1 or FIG. 3), the desorbing-concentrating gas Bxe2x80x3 (i.e., the gas which has adsorbed and separated the hydrocarbon from the treatment-object gas A in the course of its passage through the adsorbent layer 9) past the adsorbing adsorbent layer 9 of the adsorbing-desorbing recovery device 2 subsequent to its passage through the desorbing area y of the rotary adsorbing-desorbing concentration device 1 is not directly discharged into the atmosphere. Instead, the desorbing-concentrating gas Bxe2x80x3 is returned via the desorbing-concentrating gas return passage 12 back to the adsorbing area x of the rotary adsorbing-desorbing concentration device 1 together with the treatment-object gas A which is greater in amount than the gas Bxe2x80x3, such that both the gaseous hydrocarbon remaining within the returned desorbing-concentrating gas Bxe2x80x3 and the gaseous hydrocarbon contained in the large amount of new treatment-object gas A are adsorbed and separated in the course of passage through the adsorbing area x of the rotary adsorbing-desorbing concentration device 1 (more particularly, during the passage through the rotor at its adsorbing area x), and this mixture gas after the treatment is discharged as treated treatment-object gas Axe2x80x2 into the atmosphere.
Therefore, the adsorbing-desorbing recovery device 2 needs not to reduce the hydrocarbon concentration of the desorbing-concentrating gas Bxe2x80x2 (concentrating gas) sent from the desorbing area y of the rotary adsorbing-desorbing concentration device 1 to the adsorbing adsorbent layer 9 to a level low enough to allow its direct discharge into the atmosphere. For this reason, it becomes possible to reduce the treatment efficiency or capacity required of the adsorbing-desorbing recovery device 2 and hence to reduce the amount of adsorbent used in this device 2, in comparison with the conventional systems described hereinbefore. Further, it becomes also possible to reduce the temperature needed for the desorption effected by this adsorbing-desorbing recovery device 2 (e.g., to a temperature below approximately 130xc2x0 C.), so that it becomes possible to employ with such conventional heat source as steam, electric heat or the like for this desorbing process.
Incidentally, even when the hydrocarbon concentration of the treatment-object gas A slightly varies and the amount of the adsorbent used therein is fixed, the rotary adsorbing-desorbing device 1 is capable of maintaining the concentration of the hydrocarbon remaining in the treated treatment-object gas Axe2x80x2 fed from the adsorbing area x as long as the amount of the treatment-object gas does not vary significantly, provided that its operational condition is appropriately adjusted by, for example, adjusting the rotational speed of its rotor to an optimum condition suited for a particular hydrocarbon concentration which is then present. For this reason, when the desorbing-concentrating gas Bxe2x80x3 sent from the adsorbing-desorbing recovery device 2 with its treatment efficiency reduced as described above (i.e., a small amount of gas still having high concentration of hydrocarbon) is caused to pass the adsorbing area x of the rotary adsorbing-desorbing concentration device 1 together with the large amount of treatment-object gas A, the concentration of the hydrocarbon remaining in the treated gas Axe2x80x2 obtained from its adsorbing area x may be maintained substantially as low as the concentration of hydrocarbon that would be achieved if the treatment-object gas A alone were caused to pass the adsorbing area x (i.e., low value allowing gas discharge into the atmosphere).
For the reasons described above, according to the present invention it has become possible to achieve compactness of the system and reduction in energy consumption while retaining high recovery efficiency of the gaseous hydrocarbon, as compared with the conventional systems. Moreover, it has become also possible to reduce the desorbing temperature, thus restricting degradation in the quality of adsorbent, improving the service life of the system and promoting the recovery efficiency of the hydrocarbon with effective prevention of unfavorable change in the quality of hydrocarbon to be recovered.
According to the present invention (see FIG. 1), the above-described system according to the invention may further comprise: a desorbing-recovering gas recycling passage 16 for returning the desorbing-recovering gas Cxe2x80x2 past the desorbing adsorbent layer 9 back to the desorbing adsorbent layer 9 causing it to pass again the layer 9; and
a desorbing-recovering gas return passage 19 for taking off from the desorbing-recovering gas recycling passage 16 an amount of the desorbing-recovering gas Cxe2x80x2 corresponding to an amount of fresh desorbing-recovering gas Ci to be newly supplemented to this desorbing-recovering gas recycling passage 16 and then returning this taken-off desorbing-recovering gas Cr via the concentrating device 3 back to the adsorbing adsorbent layer 9 for causing the taken-off desorbing-recovering gas Cr to pass the adsorbing adsorbent layer 9 together with the desorbing-concentrating gas Bxe2x80x2 past the desorbing area y.
That is to say, according to the above-described construction (see FIG. 1), for the purpose of elevating the cooling temperature needed by the condensing recovery device 3 (i.e., elevating it up to substantially the room temperature), the amount of the desorbing-recovering the gas Cr taken off from the desorbing-recovering gas recycling passage 16 is returned via the condensing recovery device 3 back to the adsorbing adsorbent layer 9 of the adsorbing-desorbing recovery device 2 (i.e., a relatively high concentration of un-condensed gaseous hydrocarbon is allowed to remain in the taken-off desorbing-recovering gas Cr past the concentrating device 3). In doing so, the desorbing-concentrating gas Bxe2x80x3 which has passed the adsorbing adsorbent layer 9 together with the taken-off desorbing-recovering gas Cr past the condensing device is returned via the desorbing-concentrating gas return passage 12 to the adsorbing area x of the rotary adsorbing-desorbing concentration device 1 for its further treatment. Hence, in comparison with the construction in which this desorbing-concentrating gas Bxe2x80x3 past the adsorbent layer is directly discharged into the atmosphere, the temperature needed for gas cooling process in the condensing recovery device 3 may be further elevated, so that it becomes possible to effect this gas cooling process by using such conventional means as cooling water (so-called room temperature cooling).
For the reasons above, the system may be still superior in energy saving performance, with the additional effect of reduction in the desorbing temperature described above.
Also, in the above construction, the condensing recovery device 3 needs to process only a very small amount of desorbing-recovering gas Cr taken off from the desorbing-recovering gas recycling passage 16 (the amount corresponding to the amount of fresh desorbing-recovering gas Ci to be supplemented to this desorbing-recovering gas recycling passage 16). Therefore, in comparison with a construction in which the entire amount of desorbing-recovering gas Cxe2x80x2 recycled by the desorbing-recovering gas recycling passage 16 is caused to pass the condensing recovery device 3 to be heated again for solvent desorption after this passage, it is possible to reduce wasteful use of heat due to repetition of cooling and heating cycles, so that a small-capacity and size device may be employed as this condensing recovery device 3.
According to the present invention (see FIG. 3), the above-described system according to the invention may further comprise: a desorbing-recovering gas recycling passage 16 for returning the desorbing-recovering gas Cxe2x80x2 past the desorbing adsorbent layer 9 back to the desorbing adsorbent layer 9 causing it to pass again the layer 9; and
a desorbing-recovering gas return passage 19 for taking off, from a portion of the desorbing-recovering gas recycling passage 16 downstream of the condensing device 3, an amount of the desorbing-recovering gas Cxe2x80x2 corresponding to an amount of fresh desorbing-recovering gas Ci to be newly supplemented to this desorbing-recovering gas recycling passage 16 and then returning this taken-off desorbing-recovering gas Crxe2x80x2 back to the adsorbing adsorbent layer 9 for causing the taken-off desorbing-recovering gas Crxe2x80x2 together with the desorbing-concentrating gas Bxe2x80x2 past the desorbing area y to pass the adsorbing adsorbent layer 9.
That is to say, according to the above-described construction (see FIG. 3), for the purpose of elevating the cooling temperature needed by the condensing recovery device 3 (elevating it up to substantially the room temperature), the amount of desorbing-recovering gas Crxe2x80x2 taken off from a portion of the desorbing-recovering gas recycling passage 16 downstream of the condensing device 3 is returned back to the adsorbing adsorbent layer 9 of the adsorbing-desorbing recovery device 2 (i.e., a relatively high concentration of un-condensed gaseous hydrocarbon is allowed to remain in the taken-off desorbing-recovering gas Crxe2x80x2 past the condensing device 3). In doing so, the desorbing-concentrating gas Bxe2x80x3 which has passed the adsorbing adsorbent layer 9 together with the taken-off desorbing-recovering gas Crxe2x80x2 past the condensing device 3 is returned via the desorbing-concentrating gas return passage 12 to the adsorbing area x of the rotary adsorbing-desorbing concentration device 1 for its further treatment. Further, as the treatment efficiency of the adsorbing-desorbing recovery device 2 may be reduced for allowing a higher concentration of the un-condensed hydrocarbon in the desorbing-recovering gas C to be recycled to the desorbing adsorbent layer 9 subsequent its passage through the condensing device 3, the temperature needed for the gas cooling process at the condensing recovery device 3 may be further elevated, in comparison with the case of directly discharging the desorbing-concentrating gas Bxe2x80x3 past the adsorbent layer into the atmosphere, so that this gas cooling process may be effected by using such conventional means as cooling water (so-called room temperature cooling).
For the reasons above, this system like the above-described system, may be still superior in energy saving performance, with the additional effect of reduction in the desorbing temperature.
Also, in the above construction, the desorbing-recovering gas C whose hydrocarbon concentration has been reduced in the course of its passage through the condensing recovery device 3 is returned to the desorbing adsorbent layer 9 for desorption, the desorption efficiency of the adsorbing-desorbing recovery device 2 may be improved.
According to the present invention (see FIG. 1 or FIG. 3), in the system according to any one of the above-described systems the hydrocarbon concentration of the desorbing-concentrating gas Bxe2x80x3 to be returned to the adsorbing area x via the desorbing-concentrating gas return passage 12 is set approximately equal to or higher than the hydrocarbon concentration of the treatment-object gas A.
That is to say, with such setting of the hydrocarbon concentration of the desorbing-concentrating gas Bxe2x80x3 past the adsorbing adsorbent layer 9 to be equal to or higher than the hydrocarbon concentration of the treatment-object gas A, and by returning this desorbing-concentrating gas Bxe2x80x3 having same or higher concentration of hydrocarbon as or than the treatment-object gas A via the desorbing-concentrating gas return passage 12 to the adsorbing area x of the rotary adsorbing-desorbing concentration device 1, the treatment efficiency required of the adsorbing-desorbing recovery device 2 may be further reduced, in comparison with the case where desorbing-concentrating gas Bxe2x80x3 having lower hydrocarbon concentration than the treatment-object gas A is returned to the adsorbing area x. Further, when this construction is implemented in the system according to section [2] or [3] above the cooling temperature needed at the adsorbing-desorbing recovery device 2 may be further elevated, so that the effects of the invention may be achieved more conspicuously. Hence, the advantageous reduction in the system size and energy consumption may be achieved more effectively.
Further and other features and effects of the invention will become apparent upon reading the following description of the preferred embodiments thereof with reference to the accompanying drawings.